The pre sent invention relates to methods and compositions for inhibiting the activity of telomerase enzyme.
Nearly all bodily cells possess finite capacity to divide and replicate. One mechanism that regulates this finite life span involves telomeres, which are specialized structures found at the end of chromosomes and composed of protein and DNA having the repeated sequence, TTAGGG. Telomeres shorten each time a cell divides until they critically short. This event is associated with the onset of cell senescence, after which the senescent cell ceases to proliferate.
In contrast, certain cells are “immortal” and have the capacity to divide indefinitely. Such cells include, for example, single-celled eukaryotic organisms, germline cells (i.e., oocytes and sperm), certain human cell cultures and cancer cells. These cells do not exhibit telomere shortening upon cell division. Most of these cells, including about 90% of primary cancers, exhibit the activity of an enzyme, telomerase. Mortal bodily cells exhibit very little or no telomerase activity. The amount of hTR in cancer cell lines is two- to seven-fold higher than the amount in normal cells (Feng et al., supra).
Telomerase is a ribonucleoprotein that regulates the length of telomeres. Telomerase acts as a DNA polymerase, adding telomeric repeat sequences to the chromosomes' ends using a sequence within the RNA component of telomerase as a template. The RNA component of human telomerase, hTR, has been isolated. Feng et al. (1995) Science 269:1236-41 and U.S. Pat. No. 5,583,016.
Inhibiting telomerase activity in immortal cells, such as cancer cells, leads to telomere shortening and cell death. Feng et al., supra, showed that transfecting an immortalized cell line, HeLa, with expression vectors that expressed hTR antisense transcripts resulted in telomere shortening and cell crisis characterized by a marked inhibition of cell growth. Thus, inhibition of telomerase activity in cancer cells is a target for therapeutic intervention.